A British Airways Boeing 777 en route from London to Chicago declared an
emergency on Oct. 5 after flight-tracking data showed its altitude fall from
36,000 ft to 9,000 ft — a drop of roughly 27,000 ft (8,230 meters) — in about
seven minutes. The aircraft turned back over Ireland, circled the Bristol
Channel for about four hours and landed at London Heathrow at about 17:00 local
time. The cause is unclear; British Airways and Heathrow had no immediate
comment.